Method and apparatus for controlling transmission power in a CDMA communication system

ABSTRACT

Method and apparatus for controlling transmission power in a closed loop power control system, wherein power control commands are based on the energy of the previous power control commands. In one embodiment, the method compares changes in the received energy of received power control commands against expected changes in those commands based on previously transmitted power control commands, and identifies suspicious responses to said previously transmitted power control commands. Hypothesis testing of the received power control commands is performed accordance any identified suspicious responses.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to communications. More particularly, thepresent invention relates to a novel and improved method and apparatusfor controlling the power of a CDMA transmitter.

II. Description of the Related Art

The use of code division multiple access (CDMA) modulation-techniques isone of several techniques for facilitating communications in which alarge number of system users are present. Other multiple accesscommunication system techniques, such as time division multiple access(TDMA) and frequency division multiple access (FDMA) are known in theart. However, the spread spectrum modulation technique of CDMA hassignificant advantages over these modulation techniques for multipleaccess communication systems. The use of CDMA techniques in a multipleaccess communication system is disclosed in U.S. Pat. No. 4,901,307,entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USINGSATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of thepresent invention, of which the disclosure thereof is incorporated byreference herein. The use of CDMA techniques in a multiple accesscommunication system is further disclosed in U.S. Pat. No. 5,103,459,entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMACELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the presentinvention, of which the disclosure thereof is incorporated by referenceherein.

CDMA by its inherent nature of being a wideband signal offers a form offrequency diversity by spreading the signal energy over a widebandwidth. Therefore, frequency selective fading affects only a smallpart of the CDMA signal bandwidth. Space or path diversity is obtainedby providing multiple signal paths through simultaneous links from amobile user through two or more cell-sites. Furthermore, path diversitymay be obtained by exploiting the multipath environment through spreadspectrum processing by allowing a signal arriving with differentpropagation delays to be received and processed separately. Examples ofpath diversity are illustrated in U.S. Pat. No. 5,101,501 entitled“METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN ACDMA CELLULAR TELEPHONE SYSTEM”, and U.S. Pat. No. 5,109,390 entitled“DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assignedto the assignee of the present invention and incorporated by referenceherein.

A method for transmission of speech in digital communication systemsthat offers particular advantages in increasing capacity whilemaintaining high quality of perceived speech is by the use of variablerate speech encoding. The method and apparatus of a particularly usefulvariable rate speech encoder is described in detail in U.S. Pat. No.5,414,796, entitled “VARIABLE RATE VOCODER”, assigned to the assignee ofthe present invention and incorporated by reference herein.

The use of a variable rate speech encoder provides for data frames ofmaximum speech data capacity when said speech encoding is providingspeech data at a maximum rate. When a variable rate speech coder isproviding speech data at a less than maximum rate, there is excesscapacity in the transmission frames. A method for transmittingadditional data in transmission frames of a fixed predetermined size,wherein the source of the data for the data frames is providing the dataat a variable rate is described in detail in U.S. Pat. No. 5,504,773,entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FORTRANSMISSION”, assigned to the assignee of the present invention, ofwhich the disclosure thereof is incorporated by reference herein. In theabove mentioned patent application a method and apparatus is disclosedfor combining data of differing types from different sources in a dataframe for transmission.

In frames containing less data than a predetermined capacity, powerconsumption may be lessened by transmission gating a transmissionamplifier such that only parts of the frame containing data aretransmitted. Furthermore, message collisions in a communication systemmay be reduced if the data is placed into frames in accordance with apredetermined pseudorandom process. A method and apparatus for gatingthe transmission and for positioning the data in the frames is disclosedin U.S. Pat. No. 5,659,569, entitled “DATA BURST RANDOMIZER”, assignedto the assignee of the present invention, of which the disclosurethereof is incorporated by reference herein.

A useful method of power control of a mobile in a communication systemis to monitor the power of the received signal from the mobile stationat a base station. The base station in response to the monitored powerlevel transmits power control bits to the mobile station at regularintervals. A method and apparatus for controlling transmission power inthis fashion is disclosed in U.S. Pat. No. 5,056,109, entitled “METHODAND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULARMOBILE TELEPHONE SYSTEM”, assigned to the assignee of the presentinvention, of which the disclosure thereof is incorporated by referenceherein.

In a communication system that provides data using a QPSK modulationformat, very useful information can be obtained by taking the crossproduct of the I and Q components of the QPSK signal. By knowing therelative phases of the two components, one can determine roughly thevelocity of the mobile station in relation to the base station. Adescription of a circuit for determining the cross product of the I andQ components in a QPSK modulation communication system is disclosed inU.S. Pat. No. 5,506,865, entitled “PILOT CARRIER DOT PRODUCT CIRCUIT”,assigned to the assignee of the present invention, the disclosure ofwhich is incorporated by reference herein.

There has been an increasing demand for wireless communications systemsto be able to transmit digital information at high rates. One method forsending high rate digital data from a remote station to a central basestation is to allow the remote station to send the data using spreadspectrum techniques of CDMA. One method that is proposed is to allow theremote station to transmit its information using a small set oforthogonal channels, this method is described in detail in U.S. Pat. No.6,396,804, entitled “HIGH DATA RATE CDMA WIRELESS COMMUNICATION SYSTEM”,assigned to the assignee of the present invention and incorporated byreference herein.

SUMMARY OF THE INVENTION

The present invention is a novel and improved method and apparatus forcontrolling the transmission power in a closed loop power controlsystem. In the present invention, power control commands punctured intothe forward link traffic signal are used to determine the sufficiency ofthe energy of forward link traffic signal. In the present invention anovel method of closed loop power control is proposed which makes use ofthe energy of power control symbols, power control command estimationsas well as traffic signal energy measurements to achieve greateraccuracy of the closed loop power control system.

The drawback of using the power control symbols alone to determine thesufficiency of the traffic channel transmission energy is that there arenot a lot of power control symbols and thus they are susceptible to theinfluence of the noise added to the power control symbols. Thissituation is further complicated because the energy of the power controlsymbols cannot simply be averaged together because they each may havebeen transmitted at different energies due to the response to powercontrol commands. This situation is even further complicated becausepower control commands may be received incorrectly by the transmittingdevice.

The present invention provides effective methods of estimating signalquality of a received CDMA signal by means of combining power controlsymbol measurements and traffic channel estimations.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of the base station of the present invention;

FIG. 2 is a flowchart illustrating the method for generating the powercontrol commands of the first exemplary embodiment of the presentinvention;

FIGS. 3A-3D illustrate the methods for generating the synthesizedwaveforms used to determine the power control bits of the presentinvention;

FIG. 4 is a block diagram illustrating the mobile station of the firstexemplary embodiment of the present invention wherein the power controlcommands are generated in accordance with systematically corrected powercontrol commands; and

FIG. 5 is a block diagram illustrating the mobile station of the secondexemplary embodiment of the present invention wherein the power controlcommands are generated in accordance with energy weighted power controlcommands;

FIG. 6 is a flowchart illustrating a sub-optimal method for correctingthe closed loop power control commands which reduces computationalcomplexity; and

FIGS. 7A-7C illustrate the difficulties that are associated in adjustingthe power control commands in order to average their energies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

FIG. 1 illustrates the exemplary embodiment of the base station of thepresent invention. The present invention is described in terms offorward link power control. It will be understood by one skilled in theart that the present invention is equally applicable to reverse linkpower control. In addition, the present invention is equally applicableto any variable rate communication system employing closed loop powercontrol. A frame of data is provided to CRC and tail bit generator 2.CRC and tail bit generator 2 generates and a set of cyclic redundancycheck (CRC) bits and a set of tail bits and appends those bits to theinput frame of data. The frame of data with CRC and tail bits isprovided to encoder 4. Encoder 4 provides forward error correctioncoding on the frame of data including the CRC and tail bits. Encoder 4could, for example, be a convolutional encoder or a turbo encoder orother forward error correction coder, the design and implementation ofwhich are well known in the art.

The encoded symbols are then provided to interleaver 6, which reordersthe encoded symbols in accordance with a predetermined interleaverformat. In addition, interleaver 6 provides redundancy in the encodedsymbols such that the resultant output consists of a fixed number oforiginal encoded symbol versions and repeated versions of the encodedsymbols. The reordered symbols are provided to spreading element 8,which scrambles the data in accordance with a long code pseudorandomsequence. The scrambled symbols are then provided to de-multiplexer 10.De-multiplexer 10 maps the symbols into a four point constellationconsisting of (1,1), (1,−1), (−1,−1) and (−1,−1).

De-multiplexer 10 provides the symbols to data gain elements 20 a and 20b. Data gain elements 20 a and 20 b adjust the energy of symbols on thetwo output signals and provide the gain adjusted signals to puncturingelements 24 a and 24 b, respectively. In the exemplary embodiment, thetraffic data varies in transmission rate on a frame to frame basis. Thetransmission energy is varied in proportion to the data rate of thetraffic data. For example, if a traffic data frame is transmitted at apredetermined maximum rate, then the signal containing the traffic dataframe would be transmitted at a predetermined maximum transmissionenergy. If a traffic data frame was transmitted at a rate equal to halfof the predetermined maximum rate, then the signal containing thetraffic data frame would be transmitted at half of the predeterminedmaximum transmission energy, and so on. Because of the redundancyintroduced by interleaver 6, the resulting symbol energy of the energyscaled signal remains constant.

Puncturing elements 24 a and 24 b insert reverse link power control bitsinto the gain adjusted data signals. The outgoing power control bits areprovided to power control gain element 22. In the exemplary embodiment,the power control bits are always transmitted at the predeterminedmaximum transmission energy of the traffic channel regardless of therate of the traffic data. Because the power control bits are not scaledin accordance with rate, these symbols offer a means of evaluating thesufficiency of the received traffic signal without knowledge of the rateof the traffic data. The gain adjusted power control bits are providedto puncturing elements 24 a and 24 b and are punctured into the outgoingtraffic channels.

The signals from puncturing elements 24 a and 24 b are provided to afirst input of orthogonal covering elements 26 a and 26 b. A trafficchannel orthogonal covering sequence is generated by traffic Walshgenerator 28. The Walsh sequence is provided to orthogonal coveringelements 26 a and 26 b and provides an orthogonal covering on theoutgoing traffic signal. The orthogonally covered traffic signal isprovided to summer 18. For the sake of simplicity the generation of asingle orthogonal traffic channel is illustrated. It will be understoodby one skilled in the art that in commercial implementations, many moreidentically implemented traffic channels will also be present andsupplying their orthogonally covered data to summer 18.

In the exemplary embodiment, a code division pilot is transmitted alongwith the traffic channels to allow for coherent demodulation of thetransmitted traffic signals. Pilot symbols are provided de-multiplexer12 which maps the pilot symbols into a four point constellationconsisting of the points (1,1), (−1,1), (1,−1) and (−1,−1). In theexemplary embodiment, the pilot symbols consist of all zeroes. Theresultant output streams from de-multiplexer 12 are provided to a firstinput of orthogonal covering elements 14 a and 14 b.

Pilot Walsh generator 16 generates a spreading function that isorthogonal to the spreading function used to spread the traffic channeldata. In the exemplary embodiment, pilot Walsh generator 16 generatesthe Walsh(0) sequence and provides the sequence to a second input ofcovering elements 14 a and 14 b. Covering elements 14 a and 14 b coverthe de-multiplexed pilot symbols in accordance with the pilot Walshspreading function and provide the result to summer 18.

Summer 18 sums the pilot channel signal and all traffic channel signalsand provides the resultant sum signal to complex PN spreading element30. Complex PN spreading element 30 performs a spreading operation onthe input sequences that balances the load on the in-phase andquadrature channels of the transmission. Complex PN spreading element 30spreads the input signals I′ and Q′ in accordance with the equation:

I=PN _(I) ·I′+PN _(Q) ·Q′  (1)

Q=PN _(I) ·I′−PN _(Q) ·Q′,  (2)

where PN_(I) and PN_(Q) are two psuedonoise sequences, the generation ofwhich is well known in the art. The complex PN spread data sequences areprovided to transmitter 36. Transmitter 36 upconverts, filters andamplifies the signals in accordance with a QPSK modulation format andprovides the signal for transmission through antenna 38.

Signals from mobile stations in the coverage area of base station 1 arereceived at antenna, 39 and provided to receive subsystem 34. Receivesubsystem 34 demodulates and decodes the reverse link signals andoutputs the demodulated and decoded signal. In addition, receivesubsystem 34 provides a predetermined set of parameters to controlprocessor 32. Control processor 32 determines the adequacy of thereceived signal energy of the reverse link signals from each of themobile stations in communication with base station 1. Control processor32 generates a set of power control commands in and provides thecommands to puncturing elements 24 a and 24 b and operation proceeds asdescribed above.

In addition, receive subsystem 34 receives power control commands fromeach mobile station in communication with base station 1. The powercontrol commands indicate whether the base station should increase itstraffic transmission energy to the particular mobile station sending thecommands. The commands are received and provided to transmitter 36,which increases or decreases its transmission energy in responsethereto. A detailed description of closed loop power control systems isprovided in the aforementioned U.S. Pat. No. 5,056,109.

II. Power Control Based on Received Power control Commands.

In the absence of noise and when power control commands are alwaysreceived and responded to correctly, power control of the variable ratelink can be greatly simplified. However, the deleterious effects ofnoise on a signal as a result of traversing the propagation path areunavoidable as are the incorrect reception and response to power controlcommands. The present invention is designed to deal with theseadditional complexities. However, before moving on to the description ofthe present invention, it is beneficial to understand the workings of apower control system in the absence of these complexities.

Referring to FIG. 7A, FIG. 7A illustrates a received signal in whichthere is no added noise. In the first frame 510, the energy of the powercontrol commands 500 are set to a predetermined energy equal to thetransmission energy for a predetermined maximum rate. It will beunderstood by one skilled in the art that the energy of the powercontrol commands need not be transmitted at the energy of the maximumrate signal, but rather need merely have a predetermined and knownrelationship to the energy of the maximum rate signal.

The traffic energy of each frame (502 and 506) varies based on the rateof the transmitted traffic data. Providing additional symbol redundancyin the signal allows the transmitter to reduce the energy of thetransmitted traffic data. For example, if each symbol in the signal istransmitted twice, the energy at which each of the versions of thesymbols is transmitted can be approximately halved. In this fashion, thetotal energy used to transmit the symbol is kept approximately constant.This method of proportionally reducing the transmission power of asignal in response to the introduction of redundancy into the signal iswell known in the art, and is described in detail in the aforementionedU.S. Pat. No. 5,103,459.

In the present invention, the power control bits (500 and 504) remain ata constant energy that bears a known relationship to the energy of themaximum rate of the transmitted signal. Because the receiver of thepresent invention does not know a priori the rate of the transmittedsignal, it uses the energy of the received power control bits todetermine the adequacy of the energy of the received signal. This fixedpoint is important, because a signal received with redundancy may haveadequate energy to provide for reliable reception of the signal, whereasthe signal without symbol redundancy received at the same energy mayhave inadequate energy to provide reliable reception.

Because the receiver does not know the rate of the signal, oralternatively does not know the amount of symbol redundancy in thereceived signal, it cannot judge whether the received power is adequatefor reliable reception. Thus, the power control commands transmittedwith a fixed transmission power relationship to a known level of symbolredundancy provides a mean by which the receiver can assess the adequacyof the received power without knowing the rate of the traffic data.

Referring back to FIG. 7A, a receiver receiving this signal in which thepower control commands have no additive noise effects can determine thesufficiency of the energy of the received signal. In FIG. 7A, powercontrol bits 500 are punctured into the variable rate traffic data 502.In a system without additive noise effects from the propagation path,the receiver computes the energy of a single received power controlcommand 500 and compares this energy to threshold energy value. When thecomputed energy of the power control command 500 exceeds the threshold,the mobile communication device determines that the energy of thereceived signal exceeds the energy which is required for reliablereception and sends back to the transmitting communication device acommand requesting that the transmitter reduce its transmission power.Conversely, when the computed energy of power control command 500 isbelow the threshold, the mobile communication device determines that theenergy of the received signal is less than that which is required andsends back to the transmitting communication device a command requestingthat the transmitter increase its transmission power. I Althoughdescribed in the context of simple up/down power control commands theteachings are easily extending to multi-bit power control commands thatare indicative of the direction and amount of change in transmissionpower.

FIG. 7B introduces the additional complexity of additive noise into thereceived signal. When noise is introduced, it is no longer reliable todetermine the sufficiency of the received signal using single powercontrol bits. Power control bits are very short in duration and evenminor changes in the propagation path can result in serious degradationof the received energy estimate.

When noise is added to the power control symbols 600, it is desirable todetermine the received energy averaged across a plurality of powercontrol bits 600 in order to reduce the effect of noise on the receivedpower control bits 600. In its simplest form the power control bits 600may simply be averaged together using a moving average filter to providean improved estimate of the received energy. In a preferred embodiment,the more recently received power control symbols are emphasized. Thiscombining can be performed using FIR filters or IIR filters theimplementation and design of which are well known in the art.

FIG. 7C illustrates the additional complexity wherein the transmissionpower of the transmitted signal varies in a known fashion in response toclosed loop power control commands transmitted from the mobile station.For simplicity of illustration the noise effects illustrated in FIG. 7Bhave been removed. The noise effects would be present in any systems andthe description will apply when noise is present and as described aboveare the motivation for averaging multiple power control commands priorto determining the adequacy of the received signal.

It is not appropriate in the determination of the adequacy of thereceived signal in FIG. 7C to simply average the energy of the receivedpower control commands. This is because the transmission energies havevaried in response to power control commands transmitted by the mobilestation in addition to changes in the propagation path.

Power control command 700 and traffic symbols 702 make up a powercontrol group (PC Group 1). That is to say, they were transmitted basedon the same set of power control commands received at the base station.Similarly, power control command 704 and traffic symbols 706 comprisepower control group 2 (PC Group 2), power control command 708 andtraffic symbols 710 comprise power control group 3 (PC Group 3), andpower control command 712 and traffic symbols 714 comprise power controlgroup 4 (PC Group 4).

The mobile station knows the power control commands that have caused thechanges in transmission power of the base station, because the mobilestation transmitted those commands. In this simplified system, theassumption is that all power control commands transmitted by the mobilestation are received correctly by the base station and responded to in aknown fashion. Thus, the mobile station can remove the effects on thereceived power control commands that result from the closed loop powercontrol system and thus can average the power control commands togetherin a meaningful way that reflects the changes in the propagation pathalone.

In this simplified system, the base station transmitter increases itstransmission power by 2Δ when it receives an up command from the mobilestation and decreases its transmission power by Δ when it receives adown command from the mobile station. Thus, when the mobile station isdetermining the adequacy of the received signal it first removes theeffects of the closed loop power control from the received commands.

The mobile station knows that the base station reduced its transmissionpower between power control group 3 and power control group 4 inresponse to a down command it transmitted. Thus, prior to averagingpower control command 712 with power control command 708, it reduces thereceived energy of power control command 708 by Δ to provide anormalized version of power control bit 708.

Similarly, the mobile station knows that it increased the transmissionpower of the base station between power control group 2 and powercontrol group 3 so prior to averaging the energy of power controlcommand 704 with the energy of power control bit 712 and the normalizedenergy of power control bit 708, the energy of power control bit 704must be normalized. First the measured energy of power control bit 704is decreased by Δ to deal with the change between power control group 3and power control group 4 and then is increase by 2Δ to deal with thechange in transmission power between power control 2 and power controlgroup 3. This results in a net summing of Δ to the measured energy ofpower control bit 704 prior to its inclusion of the power control bitenergy average.

The energy of power control group 2 is less than the energy of powercontrol group 1 in response to a down command transmitted by the mobilestation. Thus, the power control group bit 700 is modified by adding Δ,then subtracting 2Δ and then adding Δ, which results in leaving powercontrol bit 700 unchanged. The normalized versions of power control bits700, 704, 708 can then be combined or averaged with power control bit712 and the assessment of the adequacy of the received signal energy canbe performed as described with respect to FIG. 7B.

The situation is in general more complicated than that described withrespect to FIGS. 7A-7C, because there is additive noise on the powercontrol commands which are of short duration, and the power controlcommands sent by the mobile station may not have been received correctlyby the base station or the base station may not respond to the powercontrol commands as anticipated because it is using a different stepsize in response to those commands or because the base station is powersaturated.

III. Power Control Command Correction/Adjustment

FIG. 2 illustrates the first method of generating power control commandsof the present invention. In the present invention, the power controlcommands that are punctured into the forward link traffic signal areused to determine the sufficiency of the forward link traffic signal.The power control commands are used because in the present inventiontheir energy does not vary with the data rate of the traffic channel.

The drawback of using the power control commands alone to determine thesufficiency of the traffic channel transmission energy is that there arean insufficient number of power control commands and thus they areparticularly susceptible to the influence of noise on the trafficchannel. This situation is further complicated because the power controlcommands cannot simply be averaged together, because they may have beentransmitted at different energy due to the response to power controlcommands from the mobile station. This situation is even furthercomplicated because power control commands transmitted from the mobilestation may be received incorrectly by the base station 1. The situationis further complicated because a station might choose to partially ortotally ignore a power control command received from the mobile station.All the problems outlined above can be solved by means of the methods ofthe present invention.

The mobile station can determine the delay between it and base station 1and more particularly the mobile station knows the time interval betweenit transmitting a power control command and the mobile station receivingthe forward link signals gain adjusted in response to the power controlbits. In block 50, the mobile station identifies possibly incorrectlyreceived power control commands. Turning to FIGS. 3A-3C, FIG. 3Areflects the order of power control commands transmitted by the mobilestation. FIG. 3B illustrates the received forward link traffic signalsadjusted in response to the power control commands illustrated in FIG.3A. FIG. 3C illustrates the identification of suspicious responses bybase station 1 to the power control commands transmitted by the mobilestation.

In FIG. 3A, the sequence of power control commands transmitted by themobile station. The mobile station first transmitted a “down” command800, followed by “up” command 802, “up” command 804, “down” command 806,“up” command 808, “down” command 810, “down” command 812, “up” command814 and “up command 816.

In FIG. 3B, the delayed received responses to the power control commands(as received) are illustrated. The first power control group comprisesthe reverse link power control command 818 and the forward link trafficdata or pilot symbols 820. A power control group is defined herein as aninterval of the forward link signal in which there are no changes totransmission energy within that interval. That is to say that theforward link transmitter has not varied its transmission energy based onany intervening power control commands over the interval of reverse linkpower control command 818 and the forward link traffic data or pilotsymbols 820. In other words, the transmission energy of each powercontrol group is based on the same set of received closed loop powercontrol commands.

The first power control group in the forward link 901 consists of powercontrol command 818 and traffic data or pilot symbols 820; the secondpower control group 902 consists of power control command 822 andtraffic data or pilot symbols 824; the third power control group 903consists of power control command 826 and traffic data or pilot symbols828; the fourth power control group 904 consists of power controlcommand 830 and traffic data or pilot symbols 832; the fifth powercontrol group 905 consists of power control command 834 and taffic dataor pilot symbols 836; the sixth power control group 906 consists ofpower control command 838 and traffic data or pilot symbols 840; theseventh power control group 907 consists of powe control command 842 andtraffic data or pilot symbols 844; the eighth power control group 908consists of power control command 846 and traffic data or pilot symbols848; the ninth power control group 909 consists of power control command850 and traffic data or pilot symbols 852; and the tenth power controlgroup 910 consists of power control command 854 and traffic data orpilot symbols 856.

In the exemplary embodiment, the power control group begins with a powercontrol command and is followed by traffic data. This requires that thefeedback rate of power control commands on the forward and reverse linksbe identical. The present invention is not limited to applications wherethe feedback rate of the forward and reverse link power control commandsare the same. Moreover, there is no requirement that the power controlcommands being corrected be multiplexed into the traffic or pilot symboldata. These characteristics are simply put in for illustrative purposesto show the present invention applied to the proposed cdmda2000 RTTcandidate submission.

The mobile station transmitted “Down” command 800 and monitors theforward link signal illustrated in FIG. 3B to identify the expectedresponse to that command. Specifically, the mobile station anticipates adecrease in the energy between the power control group 901 and powercontrol group 902 in response to the “Down” power control command 800.The mobile station anticipates an increase in the energy between powercontrol group 902 and power control group 903 in response to the “Up”command 802. The mobile station anticipates an increase in the energybetween power control group 903 and power control group 904 in responseto the “Up” command 804. The mobile station anticipates a decrease inthe energy between power control group 904 and power control group 905in response to the “Down” command 806. The mobile station anticipates anincrease in the energy between power control group 905 and power controlgroup 906 in response to the “Up” command 808. The mobile stationanticipates a decrease in the energy between power control group 906 andpower control group 907 in response to the “Down” command 810. Themobile station anticipates a decrease in the energy between powercontrol group 907 and power control group 908 in response to the “Down”command 812. The mobile station anticipates an increase in the energybetween power control group 908 and power control group 909 in responseto the “Down” command 814. The mobile station anticipates an increase inthe energy between power control group 909 and power control group 910in response to the “Up” command 816.

In FIG. 3C, suspicious changes in the received energy are flagged. Thosethat are suspicious are marked with an “X”, while those appear to beconsistent with the power control commands are marked with an “O”. Thechange in received energy between power control groups 901 and 902 isconsistent with “down” command 800, so this transition is marked as notsuspicious in metric 858. The change in received energy between powercontrol groups 902 and 903 is inconsistent with “up” command 802, sothis transition is marked as suspicious in metric 860. The change inreceived energy between power control groups 903 and 904 is consistentwith “up” command 804, so this transition is marked as not suspicious inmetric 862. The change in received energy between power control groups904 and 905 is consistent with “down” command 806, so this transition ismarked as not suspicious in metric 864. The change in received energybetween power control groups 905 and 906 is consistent with “up” command808, so this transition is marked as not suspicious in metric 866. Thechange in received energy between power control groups 906 and 907 isconsistent with “down” command 810, so this transition is marked as notsuspicious in metric 868. The change in received energy between powercontrol groups 907 and 908 is consistent with “down” command 812, sothis transition is marked as not suspicious in metric 870. The change inreceived energy between power control groups 908 and 909 is inconsistentwith “up” command 814, so this transition is marked as suspicious inmetric 872. Lastly, the change in received energy between power controlgroups 909 and 910 is consistent with “up” command 816, so thistransition is marked as not suspicious in metric 874.

In the preferred embodiment, traffic energies are used to identify thesuspicious power control bits, because the total energy in all of thetraffic symbols is greater than in the power control bits. For this useof traffic energies, the rate need not be known.

After identifying all suspicious power control bits, a set of test powercontrol vectors are generated in block 52. Referring to FIG. 3C, it canbe seen that the set of vectors to test would include four test vectorsof potential power control commands as received by base station 1. Thefour potential power control command sets as received by base station 1would include:

D U U D U D D U U

D D U D U D D U U

D U U D U D D D U  (3)

D D U D U D D D U

These four possible sequences of receive power control commands wouldeach then be tested to determine which sequence of power controlcommands would result in a transmission signal closest matching thatreceived.

FIG. 3D illustrates the construction of a synthesized waveform based onthe possible power control command sequences in equation (3) above. Themobile station attempts to determine a waveform that would, most closelyresemble the received waveform in FIG. 3B under different hypothesesregarding potential errors in the reception of power control commands bythe base station.

In FIG. 3D illustrates an a test waveform based on the assumption thatthe second power control command 802 was received in error by the basestation. Thus, a waveform is synthesized based on the hypothesis thatthe sequence of power control commands received by the base station was“Down”, “Down”, “Up”, “Down”, “Up”, “Down”, “Down”, “Up”, “Up”. Intesting the hypotheses, the mobile station knows the amount the basestation will change its transmission energy in response to “up” and“down” power control commands. In the exemplary embodiment, a simpleuniform energy change (Δ)for both “up” and “down commands is presumed.In generating the test waveform power control group 922 is synthesizedat an energy level Δ below the energy of power control 921. Powercontrol group 923 is synthesized at an energy level Δ below the energylevel of power control group 922, which test the hypothesis that thesecond power control command 802 was received in error. Under theassumption that the remaining power control commands were receivedcorrectly by the base station power control group 924 is synthesized atan energy level Δ above power control group 923 reflecting the correctreception of power control command 804, power control group 925 issynthesized at an energy level Δ below power control group 924reflecting the correct reception of power control command 806, powercontrol group 926 is synthesized at an energy level Δ above powercontrol group 925 reflecting the correct reception of power controlcommand 808, power control group 927 is synthesized at an energy level Δbelow power control group 926 reflecting the correct reception of powercontrol command 810, power control group 928 is synthesized at an energylevel Δ below power control group 927 reflecting the correct receptionof power control command 812, power control group 929 is synthesized atan energy level Δ above power control group 928 reflecting the correctreception of power control command 814 and power control group 930 issynthesized at an energy level Δ above power control group 929reflecting the correct reception of power control command 816.

The initial condition 950 is varied to determine the minimum meansquared error for each test hypothesis.

In block 54, the mean squared error (MSE) for between the test powercontrol vectors and received traffic energies is computed. The meanssquare error for the ith test power control vector (MSE(i)) isdetermined in accordance with the equation: $\begin{matrix}{{{{MSE}(i)} = {\sum\limits_{j = 1}^{N}\left( {{s(j)} - {r(j)}} \right)^{2}}},} & (4)\end{matrix}$

where s(j) is the synthesized set of received power control groups basedon hypothetically received power control commands generated by the testvectors as described with respect to block 52, and r(j) are the energiesof the received power control groups.

The energy of the difference between the synthesized signal and thereceived signal is computed and stored. The initial energy is allowed tovary and the minimum mean squared error for all initial conditions foreach vector is computed. In block 56, the sequence of power controlcommands that yields the lowest mean squared error between thesynthesized signal and the received signal is selected.

In block 58, the power control commands are adjusted in accordance withthe selected power control sequence. For example, assume that the powercontrol sequence yielding the lowest mean square error is the sequence(D,U,U,D,U,D,D,U,U). Then in order to combine the power control commandsreceived by the mobile station in a meaningful fashion the adjustmentsin the transmission power of the base station in response to thosecommands must be removed.

Assume that when an “Up” command is received from the mobile station,base station 1 increases the transmission energy of the traffic channelto the mobile station is increased by ΔP_(up). When a “Down” command isreceived from the mobile station, base station 1 increases thetransmission energy of the traffic channel to the mobile station isdecreased by ΔP_(down). Assume that the energy of the current receivepower control bit is P_(i), then the adjusted energy of the prior powercontrol bit should be P_(I−1)+ΔP_(up) since an up command was determinedto have been received between the current power control command and theprevious power control command. The energy of the power control bitreceived two power control intervals previous is adjusted asP_(I−1)+2·ΔP_(up) since two up commands were determined to have beenreceived between the current power control command and the power controlcommand bit received two power control groups earlier. This process ofadjusting the power control bits continues to the power control bitreceived in the first power control group.

In block 60 the adjusted energy of the power control bits is averagedtogether to remove the effects of noise on the power control bits. Inblock 62, the average adjusted energy of the power control bit sequenceis compared against a threshold. In block 64, if the average adjustedenergy of the power control bit sequence is less than the threshold thena power control command indicating that the base station should increasethe transmission energy of the traffic channel is generated. If theaverage adjusted energy of the power control bit sequence is greaterthan the threshold then a power control command indicating that the basestation should decrease the transmission energy of the traffic channelis generated.

FIG. 6 is a flowchart illustrating a sub-optimal search algorithm thatreduces the computational complexity of the power control bit correctionalgorithm illustrated in FIG. 2. The method illustrated in FIG. 6identifies the suspicious power control commands and changes eachsuspicious power control command one at a time. The changed powercontrol command that result in the lower mean squared error is thenfixed and the remaining suspicious power control commands are changed todetermine the change that results in the greatest reduction in theenergy between the received frame and the synthesized frame.

In block 300, the K power control commands that are identified to bemost likely in error are identified. In block 302, K synthesized powercontrol groups are generated. In block 304, the mean squared errorbetween the synthesized power control groups and the received signal iscomputed for each of the K power control group hypotheses in accordancewith equation (4) above.

In block 306, the synthesized power control group with the lowest meansquared error is selected. In block 308, the original frame is set to beequal to the selected synthesized frame. In block 308 the power controlcommand that was changed in the selected synthesized frame is fixed andthe received frame of data is replaced with the selected synthesizedframe. In block 310, the power control command that was changed in theselected synthesized frame is eliminated from the list of suspiciouspower control commands.

Control block 312 tests to determine whether the maximum number ofiterations has been reached. If the maximum number of iterations hasbeen reached, then the process is halted and the adjusted power controlcommand set selected. If the maximum number of iterations has not beenreached, then the process moves to block 316 where the number ofsuspicious commands to be searched is reduced by one. The process thenproceeds to block 302 and the operation proceeds as describedpreviously.

It should be noted that although the previous descriptions are based onthe traffic energies the process can be performed on the punctured powercontrol bits alone.

FIG. 4 illustrates the mobile station incorporating the power controlcommand generation system of the present invention. Signals are receivedat antenna 100 and provided through duplexer 102 to receiver 104.Receiver 104 down converts, filters and amplifies the received signal inaccordance with a QPSK demodulation format. The in-phase and quadraturecomponents of the demodulated signals are provided to complex PNDe-Spreader 106.

Complex PN De-Spreader 106 despreads the received signal in a accordancewith the pseudonoise sequences PN_(I) and PN_(Q). The PN despreadsignals are provided to a first input of orthogonal despreaders 108 aand 108 b and to pilot filter 114. In the exemplary embodiment, whereWalsh (0) is used to cover the pilot symbols, pilot filter 114 cansimply be a low pass filter. In cases where other Walsh sequences areused to cover the pilot symbols the Walsh covering is removed by pilotfilter 114.

Walsh sequence generator 110 generates a replica of the orthogonalsequence used to cover the traffic channel and provides the sequence toa second input of orthogonal despreaders 108 a and 108 b. Orthogonaldespreaders 108 a and 108 b remove the traffic channel Walsh coveringand provide the result to dot product circuit 112. Dot product circuit112 computes the dot product of the uncovered traffic channel and thepilot channel to remove phase ambiguities from the received signal.

The resulting scalar sequence on the I and Q channels are provided tode-multiplexer 116. De multiplexer 116 removes the received powercontrol bits from the received signals and provides those bits to powercontrol bit processor 120. The traffic signals are provided to energycomputation means 118 which squares the amplitude samples and sums theresults to yield a value indicative of the energy of the demodulatedsignal. The energy of the signal for a particular power control group isprovided to control processor 122.

Control processor 122 performs the computations described in block 50,52, 54 and 56 of FIG. 1. Control processor 122 provides a signalindicative of the correction to the energies of the received powercontrol symbols to power control bit processor 120. Power control bitprocessor 120 adjusts the energies of the previously received powercontrol bits. And provides a signal indicative of the adjusted energiesto power control bit filter 124.

Power control bit processor 120 provides a signal indicative of theadjusted power control bit energies to power control bit filter 124.Power control bit filter 124 combines the adjusted energies of the powercontrol bits (P_(i)) in accordance with the equation: $\begin{matrix}{{P = {\sum\limits_{i = 1}^{N}{\omega_{i}P_{i}}}},} & (4)\end{matrix}$

where ω_(i) is a weighting function. This computed energy is thencompared against a threshold in power control bit generator 126. If theaverage adjusted energy of the power control bit sequence is less thanthe threshold then a power control command indicating that the basestation should increase the transmission energy of the traffic channelis generated. If the average adjusted energy of the power control bitsequence is greater than the threshold then a power control commandindicating that the base station should decrease the transmission energyof the traffic channel is generated.

The generated power control command is provided to transmit subsystem128 which combines the power control bit with the reverse link signaland provides the signal through duplexer 102 for transmission to basestation 1 through antenna 100.

II. Traffic Weighting of Power Control Bits

In a second method for providing an averaged value of the power controlbit energies, the power control bits are weighted and averaged inaccordance with the energy of the traffic in the power control group.This method makes no attempt to determine whether the power controlcommands were received correctly or even the size of the step. Thus,this second embodiment is particularly robust. The second embodiment,weights the energy of the power control symbols in accordance with thereceived energy of the traffic data. In its simplest form this isrealized by a moving average filter. In this second embodiment, the rateof the traffic signal must not change over the filtering window. Thus,if the rate of the traffic data can change only on frame boundaries, thefiltering operation must be performed on power control groups within agiven frame. In a system where the rate changes on frame boundaries, thefilter must reset on frame boundaries.

The filtered power control bit energy for the Nth power control group({circumflex over (P)}_(N)) is determined in accordance: $\begin{matrix}{{{\hat{P}}_{N} = {\sum\limits_{i = 1}^{N}{{\beta_{i}\left( \frac{T_{N}}{T_{i}} \right)}P_{i}}}},} & (5)\end{matrix}$

where T_(i) is the traffic energy for ith power control group, T_(N) isthe traffic energy for Nth power control group, P_(i) is the powercontrol bit energy of the ith power control group, and β is a weightingfunction. $\begin{matrix}{{\beta_{i} = \frac{T_{i}}{\sum\limits_{n = 1}^{N}T_{n}}},} & (6)\end{matrix}$

which leads to: $\begin{matrix}{{{\hat{P}}_{N} = \frac{T_{N}{\sum\limits_{i = 1}^{N}P_{i}}}{\sum\limits_{i = 1}^{N}T_{i}}},} & (7)\end{matrix}$

and a further improvement is to use the least squares estimate of thefinal traffic energy: $\begin{matrix}{{\hat{P}}_{N} = \frac{\left( T_{N} \right)_{{least}\quad {{sq}.\quad {estimate}}}{\sum\limits_{i = 1}^{N}P_{i}}}{\sum\limits_{i = 1}^{N}T_{i}}} & (8)\end{matrix}$

In the exemplary embodiment, the forward link signal is generated asdescribed with respect to FIG. 1. In FIG. 5, signals are received atantenna 200 and provided through duplexer 202 to receiver 204. Receiver204 down converts, filters and amplifies the received signal inaccordance with a QPSK demodulation format. The in-phase and quadraturecomponents of the demodulated signals are provided to complex PNDe-Spreader 206.

Complex PN De-Spreader 206 despreads the received signal in accordancewith the pseudonoise sequences PN_(I) and PN_(Q). The PN despreadsignals are provided to a first input of orthogonal despreaders 208 aand 208 b and to pilot filter 214. In the exemplary embodiment, whereWalsh (0) is used to cover the pilot symbols, pilot filter 214 cansimply be a low pass filter. In cases where other Walsh sequences areused to cover the pilot symbols the Walsh covering is removed by pilotfilter 214.

Walsh sequence generator 210 generates a replica of the orthogonalsequence used to cover the traffic channel and provides the sequence toa second input of orthogonal despreaders 208 a and 208 b. Orthogonaldespreaders 208 a and 208 b remove the traffic channel Walsh coveringand provide the results to dot product circuit 212. Dot product circuit212 computes the dot product of the uncovered traffic channel and thepilot channel to remove phase ambiguities from the received signal.

The resulting scalar sequences on the I and Q channels are provided tode-multiplexer 216. De multiplexer 216 removes the received powercontrol bits from the received signals and provides those bits to powercontrol bit energy calculator 220. Power control bit energy calculator220 computes the squares of the amplitudes of the received power controlbit on the I and Q channels and sums the two energy values. The powercontrol bit energy is then stored in memory element 222.

The traffic signals are provided to traffic energy calculator 218 whichsquares the amplitude of the traffic samples and sums the results toyield a value indicative of the energy of the demodulated signal. Theenergy of the traffic signal for each power control group in the frameis provided to and stored in memory 222.

Memory 222 provides the energy of the power control bits and the trafficchannel energy for each power control group in the frame to powercontrol bit filter 224. Power control bit filter computes a filteredpower control bit energy value in accordance with equation (5) above.The filtered power control bit energy is provided to power control bitgenerator 226.

The filtered power control bit energy is compared against apredetermined energy threshold in power control bit generator 226. Ifthe filtered power control bit energy is less than the threshold then apower control command indicating that the base station should increasethe transmission energy of the traffic channel is generated. If thefiltered power control bit energy is greater than the threshold then apower control command indicating that the base station should decreasethe transmission energy of the traffic channel is generated.

The generated power control command is provided to transmit subsystem228 which combines the power control bit with the reverse link signaland provides the signal through duplexer 202 for transmission to basestation 1 through antenna 200.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

We claim:
 1. In a communication system including a transmitter fortransmitting a first type of data and a second type of data wherein thesecond type of data is punctured into the first type of data, andwherein the transmission energy of said first type of data is varied inaccordance upon the rate of said first type of data and wherein thetransmission energy of said second type of data does not vary inaccordance with the rate of said first type of data, a power controlsystem for controlling the transmission energy of said first type ofdata and said second type of data comprising: receiver means forreceiving said first type of data and said second type of data;de-multiplexer means for separating said second type of data from saidfirst type of data; means for measuring an energy of said second type ofdata to provide an indication of an energy of said second type of dataas received at the receiver means; and power control processor means forreceiving said indication of the energy of said second type of data andfor generating a power control command for said transmission energy ofsaid first type of data in accordance with said indication of the energyof said second type of data.
 2. The power control system of claim 1wherein said first type of data comprises variable rate traffic data andwherein said second type of data comprises power control commands. 3.The power control system of claim 2 further comprising filter means forfiltering a plurality of said received power control commands to providean improved estimate of the received energy of said power controlcommands.
 4. The power control system of claim 3 further comprisingpower control bit processor for adjusting the energies of said receivedpower control commands to compensate for energy adjustments made at saidtransmitter in response to a set of previously transmitted power controlcommands.
 5. The power control system of claim 4 wherein said powercontrol processor is further for estimating a most likely sequence ofpower control commands responded to by said transmitter.
 6. The powercontrol system of claim 5 wherein said power control processor estimatesthe power control commands received by said transmitter and adjusts theenergies of said received power control commands to compensate forenergy adjustments made at said transmitter in response to saidestimates the power control commands received by said transmitter. 7.The power control system of claim 6 wherein said power control processorestimates said most likely sequence of power control commands respondedto by said transmitter by: comparing changes in the received energy ofsaid received power control commands against expected changes in thosecommands based on said set of previously transmitted power controlcommands; identifying suspicious responses to said previouslytransmitted power control commands; and testing a set of hypotheses ofreceive power control commands in accordance with said identifiedsuspicious responses.
 8. The power control system of claim 1 whereinsaid first type of data comprises variable rate traffic data.
 9. Thepower control system of claim 8 further comprising filter means forfiltering a set of said second type of data over a plurality of receivedframes to provide an improved estimate of the received energy of saidsecond type of data.
 10. The power control system of claim 9 furthercomprising procesor means for adjusting the energies of said second typeof data to compensate for energy adjustments made at said transmitter inresponse to a set of previously transmitted power control commands. 11.The power control system of claim 10 wherein said processor means isfurther for estimating a most likely sequence of power control commandsresponded to by said transmitter.
 12. The power control system of claim11 wherein said processor means estimates the power control commandsreceived by said transmitter and adjusts the energies of said set ofsaid second type of data over a plurality of received frames tocompensate for energy adjustments made at said transmitter in responseto said estimates the power control commands received by saidtransmitter.
 13. The power control system of claim 12 wherein said powercontrol processor estimates said most likely sequence of power controlcommands responded to by said transmitter by: comparing changes in thereceived energy of said received power control commands against expectedchanges in those commands based on said set of previously transmittedpower control commands; identifying suspicious responses to saidpreviously transmitted power control commands; and testing a set ofhypotheses of receive power control commands in accordance with saididentified suspicious responses.
 14. The power control system of claim 2further comprising filter means for filtering a plurality of saidreceived power control commands to provide an improved estimate of thereceived energy of said power control commands and wherein said filtermeans generates a filtered power control bit energy in accordance withthe equation:${{\hat{P}}_{N} = {\sum\limits_{i = 1}^{N}{{\beta_{i}\left( \frac{T_{N}}{T_{i}} \right)}P_{i}}}},$

where Ti is the traffic energy for ith power control group, Pi is thepower control bit energy of the ith power control group, and β is aweighting function.
 15. The power control system of claim 14 whereinsaid weighting function, β_(i), is determined in accordance with theequation: $\beta_{i} = {\frac{T_{i}}{\sum\limits_{n = 1}^{N}T_{n}}.}$


16. In a communication system including a transmitter for transmitting afirst type of data and a second type of data wherein the second type ofdata is punctured into the first type of data, and wherein thetransmission energy of said first type of data is varied in accordanceupon the rate of said first type of data and wherein the transmissionenergy of said second type of data does not vary in accordance with therate of said first type of data, a method for controlling thetransmission energy of said first type of data and said second type ofdata comprising: receiving said first type of data and said second typeof data; de-multiplexing said second type of data from said first typeof data; measuring an energy of said second type of data to form ameasured energy; and generating a power control command for saidtransmission energy of said first type of data in accordance with saidmeasured energy.
 17. The method of claim 16 wherein said first type ofdata comprises variable rate traffic data and wherein said second typeof data comprises power control symbols.
 18. The power control system ofclaim 17 further comprising the step of filtering the measured energy ofa plurality of said received power control symbols to provide animproved estimate of the received energy of said power control symbols.19. The method of claim 18 further comprising the step of adjusting theenergies of said received power control symbols to compensate for energyadjustments made at said transmitter in response to a set of previouslytransmitted power control commands.
 20. The method of claim 19 furthercomprising the step of estimating the most likely sequence of powercontrol commands responded to by said transmitter.
 21. The method ofclaim 20 further comprising the step of compensating for energyadjustments made at said transmitter in response to said estimates thepower control commands received by said transmitter.
 22. The method ofclaim 21 wherein said step of estimating the most likely sequence ofpower control commands responded to by said transmitter, comprises thesteps of: comparing changes in the received energy of said receivedpower control commands against expected changes in those commands basedon said set of previously transmitted power control commands;identifying suspicious responses to said previously transmitted powercontrol commands; and testing a set of hypotheses of receive powercontrol commands in accordance with said identified suspiciousresponses.
 23. The method of claim 16 wherein said first type of datacomprises variable rate traffic data.
 24. The method of claim 23 furthercomprising the step of filtering a set of said second type of data overa plurality of received frames to provide an improved estimate of thereceived energy of said second type of data.
 25. The method of claim 24further comprising adjusting the energies of said second type of data tocompensate for energy adjustments made at said transmitter in responseto a set of previously transmitted power control commands.
 26. Themethod of claim 25 wherein said processor means is further forestimating a most likely sequence of power control commands responded toby said transmitter.
 27. The method of claim 26 further comprising thesteps of: estimating the power control commands received by saidtransmitter; and adjusting the energies of said set of said second typeof data over a plurality of received frames to compensate for energyadjustments made at said transmitter in response to said estimates thepower control commands received by said transmitter.
 28. The method ofclaim 27 wherein said step of estimating the power control commandsreceived by said transmitter, comprises the steps of: comparing changesin the received energy of said received power control commands againstexpected changes in those commands based on said set of previouslytransmitted power control commands; identifying suspicious responses tosaid previously transmitted power control commands; and testing a set ofhypotheses of receive power control commands in accordance with saididentified suspicious responses.
 29. The method of claim 17 furthercomprising the step of filtering a plurality of said received powercontrol commands to provide an improved estimate of the received energyof said power control commands and wherein said filter means generates afiltered power control bit energy in accordance with the equation:${{\hat{P}}_{N} = {\sum\limits_{i = 1}^{N}{{\beta_{i}\left( \frac{T_{N}}{T_{i}} \right)}P_{i}}}},$

where Ti is the traffic energy for ith power control group, Pi is thepower control bit energy of the ith power control group, and β is aweighting function.
 30. The method of claim 29 wherein said weightingfunction β_(i), is determined in accordance with the equation:$\beta_{i} = {\frac{T_{i}}{\sum\limits_{n = 1}^{N}T_{n}}.}$